[0001] The present invention is related to a method of evaluating the condition of a given
load cell of a multiple-load cell vehicle weighing scale.
[0002] Methods for determining, during normal use, whether the load cells of a vehicle scale
are functioning properly and/or for detecting deliberate and inappropriate manipulation
of the load cells.
[0003] A typical vehicle weighing scale includes at least one scale platform (or deck) for
receiving a vehicle to be weighed. Such a scale platform is often comprised of a metal
framework with a steel plate deck, or the scale platform may be comprised of concrete
(typically enclosed within a steel frame). The scale platform is normally supported
from beneath by a number of weighing elements, such as load cells. Vehicle weighing
scales are also typically constructed with two rows of load cells aligned in the direction
of vehicle travel across the scale platform. When a vehicle is placed on the scale
platform, each load cell produces an output signal that reflects the portion of the
vehicle weight borne by that load cell. The signals from the load cells are added
to produce an indication of the total weight of the vehicle residing on the scale
platform of the weighing scale.
[0004] Vehicle weighing scales, and their associated scale platforms, can be of various
size. For example, such vehicle weighing scales are commonly of a size that is sufficient
to accommodate a multi-axle vehicle, such as a semi-truck trailer. Vehicle scales
of such size may be assembled using multiple scale platform segments (modules) that
are connected end-to-end to provide a full-length scale platform.
[0005] In the past, it has been known that a run time analysis of individual load cells
of such a vehicle weighing scale can be used to determine the health of the load cell
communication network and to record abuse. However, there has heretofore been no method
for determining, from normal use of a vehicle weighing scale, whether the load cells
of the scale are functioning properly and/or whether the load cells are being deliberately
and inappropriately manipulated, such as for the purpose of cheating in a sales transaction.
[0006] It is an objective of the present invention to provide method embodiments that allow
for a determination of one or both conditions.
[0007] Broadly speaking, method embodiments of the invention analyze the dynamically changing
patterns of measurement values seen at each load cell of a vehicle weighing scale
(hereinafter also just "scale") as a vehicle enters, remains on, and leaves the scale
platform thereof during a normal vehicle weighing operation. These dynamically changing
patterns of measurement values may be observed and documented with respect to the
load cells of a given vehicle scale when it is known that all of the load cells are
working properly and have not been tampered with, to establish a normal pattern of
load cell behavior as a vehicle enters, stops, is optionally loaded or unloaded, and
exits the scale. Subsequently, the dynamically changing patterns of measurement values
seen at the load cells of a vehicle weighing scale of interest may be compared against
an established and expected normal pattern of load cell behavior for a comparable
vehicle scale to indicate whether a given load cell measurement is believable and
internally consistent (e.g., whether a load cell of the scale of interest is operating
improperly and/or being manipulated to produce a false weight reading).
[0008] More particularly, established normal patterns of load cell behavior may be used
as operational tests. Method embodiments of the invention realize that a faulty load
cell, or a load cell that is being manipulated to produce false weight readings, will
generally fail one or more of these tests. The tests operate on the premise of the
truth of a number of assumptions, the expected (normal pattern of) behavior of the
load cells of the weighing scale during a normal vehicle weighing operation, and the
corresponding expected movement of the vehicle. The assumptions and expected behavior
of the weighing scale are associated with the scale construction and the operation
of the load cells during a normal vehicle weighing operation.
[0009] In this regard, it is first assumed that the scale is normally not loaded. That is,
a vehicle normally resides on the scale platform only during a weighing operation
or associated entry to or exit from the scale platform - otherwise the scale platform
is normally devoid of objects resting thereon. It is also initially assumed that during
a vehicle weighing operation, only a vehicle and its cargo will be weighed. It is
further assumed that vehicles to be weighed enter the scale at one end and exit at
the opposite end, with either end capable of serving as the entry point; that vehicles
do not intentionally reverse direction while on the scale platform; and that errors
will be triggered for unforeseen but perfectly legitimate reasons.
[0010] With consideration given to the aforementioned assumptions, the scale and the associated
load cells will exhibit expected normal patterns of behavior that may serve as subsequent
tests of proper operation for comparable scales. In this regard, all of the load cells
should experience at least one load-unload cycle for each vehicle weighing operation
performed. Subject to certain caveats, any load cell that does not move during a weighing
transaction is likely in error. Additionally, and also subject to certain caveats,
because a vehicle will always enter the scale from one of the two ends, one end-pair
of load cells will always be the first load cell pair to experience a load, followed
by the next pair along the path of travel of the vehicle, and so forth. Consequently,
during a normal vehicle weighing operation, load should be initially applied to the
load cells in a sequential, direction-of-travel order. Likewise, the two load cells
of a given load cell pair should simultaneously experience a left-right load.
[0011] In addition to the above-described normal patterns of behavior, it is also expected,
subject to certain caveats, that the load center of gravity associated with the vehicle
being weighed moves monotonically in the direction of travel of the vehicle while
the vehicle is on the scale platform. In other words, the load center of gravity is
generally expected to move across the scale platform starting from one end, most likely
stop, and then exit at the other end without backing up. Lastly, subject to certain
caveats, the left-right load balance should remain constant while the vehicle remains
fully on the scale platform.
[0012] Generally speaking, a mathematical model (state machine) that defines a normal pattern
of load cell behavior may be created based on the various expected states of each
load cell during a vehicle weighing operation. This allows for, among other things,
the detection of the leading edge of each loading cycle to which a load cell is subjected.
A time stamp may be stored for each load cycle leading edge. The load cell state machine
is framed by the scale gross weight being greater that its threshold weight. A controller,
such as the weighing scale controller, may be used to perform the aforementioned pattern
of behavior analysis and to thereby determine whether the load cells of the scale
are operating properly and/or to detect a deliberate manipulation of the load cells.
[0013] As described above, the load cells of a vehicle weighing scale are expected to undergo
various state transitions during a vehicle weighing operation, with the list of state
transitions defining the state machine. For example, the output (condition) of a given
load cell may transition between stable, unstable, not increasing and not decreasing
states during a weighing operation. Similarly, the gross weight reported by the load
cells of the scale may also transition between various states during a vehicle weighing
operation. These states may include stable, not decreasing, not increasing, decreasing,
and increasing states.
[0014] The state transitions begin with a vehicle entering the scale and moving on the scale
platform. The vehicle either moves to a stopped position for weighing or exits the
scale platform if the weighing operation is aborted. While the vehicle remains stopped
on the scale platform, cargo or other permissible items may be added to or removed
from the vehicle. From the stopped position, the vehicle will normally begin moving
on the scale platform once again, until the vehicle exits the scale and the scale
returns to an empty condition. All of these vehicle and vehicle-related activities
will affect the load experienced by the load cells and the weight readings produced
thereby. In other words, movement of the vehicle, stopping of the vehicle, and loading
or unloading of the vehicle will all result in the load cell state transitions that
form the state machine.
[0015] From these state transitions and the weight readings of the load cells and/or the
gross weight value resulting from the load cell weight readings, an inferred vehicle
position/state table may also be created. The vehicle position and state may be inferred
from the logical AND value of the state machine inputs listed in the columns of the
table.
[0016] The state table is reflective of the expected (normal) patterns of behavior of the
load cells and the gross weight load experienced by the scale during a normal vehicle
weighing operation. Consequently, the state conditions of the state table relating
to the gross weight and load cell conditions may be used in one regard to infer vehicle
position during a vehicle weighing operation. Alternatively, the actual pattern of
behavior of load cell conditions and the gross weight value readings observed during
a given vehicle weighing operation can be compared against the normal pattern of behavior
of the load cell conditions and the gross weight value readings as reflected in the
state table, to determine whether a given load cell measurement is believable and
internally consistent (e.g., whether a load cell is operating properly and/or being
manipulated to produce a false weight reading). The output of a faulty load cell,
or a load cell that is being manipulated to produce false weight readings, will not
match one or more of the expected state conditions listed in the state table.
[0017] The claimed invention discloses a method of evaluating the condition of a given load
cell of a multiple-load cell vehicle weighing scale, that comprises:
- identifying a dynamically changing, normal weight transfer pattern of behavior associated
with the outputs of each load cell during a typical operation of weighing a vehicle
on the vehicle weighing scale or a like vehicle weighing scale (5);
- extracting from the weight transfer patterns of behavior, the expected state condition
for each of the load cells of the scale for different vehicle positions that will
normally exist during a typical vehicle weighing operation;
- comparing the actual load cell state conditions observed during a given vehicle weighing
operation to the expected load cell state conditions; and
- analyzing the results of the comparison for each load cell to determine whether a
given load cell of the vehicle weighing scale is operating properly.
[0018] In another embodiment the method further comprises the extraction from the weight
transfer patterns of behavior, the expected state of a gross weight reading produced
by the load cells for different vehicle positions that will normally exist during
a typical vehicle weighing operation, and the comparison of the actual gross weight
reading state conditions observed during a normal vehicle weighing operation to the
expected gross weight reading state conditions.
[0019] In another embodiment of the method the expected state of each load cell output during
a given portion of a typical vehicle weighing operation is based on a plurality of
expected loading conditions, including:
- all of the load cells should experience at least one load-unload cycle per vehicle;
- the load applied by the vehicle being weighed should be initially applied to the load
cells in a sequential, direction-of-travel order;
- left-right load applied by the vehicle being weighed should be encountered by the
corresponding load cells substantially simultaneously;
- the center of gravity of the load applied by the vehicle should move monotonically
in the direction of travel; and
- the left-right load balance on the load cells should remain constant.
[0020] In a further embodiment of the method the expected state of each load cell output
during a given portion of a typical vehicle weighing operation is based on an expected
pattern of vehicle movement, the pattern of movement being:
- the vehicle enters an initially empty vehicle scale and moves along a platform of
the scale;
- the vehicle either moves to a stopped position for weighing or exits the scale platform,
with or without a temporary start and restart of movement; and
- upon leaving the stopped weighing position, the vehicle moves along the scale platform
until the vehicle exits the scale.
[0021] In a further embodiment cargo or other permissible items may be added to or removed
from the vehicle while the vehicle is in the stopped position.
[0022] In another embodiment any load cell output that does not move during a weighing operation
is considered an error.
[0023] In a further embodiment a load cell output analysis may not be performed unless the
gross weight reading value provided by the load cells is greater than a predetermined
threshold weight reading value that is representative of the load borne by the load
cells when the scale is in an unloaded state.
[0024] In another embodiment the method evaluates the operational condition a given load
cell of a vehicle weighing scale wherein the scale having a scale platform supported
from beneath by multiple load cells that are arranged in pairs in two spaced apart
rows that are aligned in the direction of normal vehicle travel across the scale platform,
the method further comprises:
- identifying a dynamically changing, normal weight transfer pattern of behavior associated
with the outputs of each load cell during a typical operation of weighing a vehicle
on the vehicle weighing scale (5) or a like vehicle weighing scale;
- extracting from the weight transfer patterns of behavior the expected state condition
for each of the load cells of the scale and the expected state of a gross weight reading
produced by the load cells, for different vehicle positions that will normally exist
during a typical vehicle weighing operation;
- using a microprocessor and associated programming to compare the actual load cell
output state conditions and the actual states of the gross weight reading produced
by the load cells during a given vehicle weighing operation to the expected load cell
output state conditions and expected states of the gross weight reading; and
- using a microprocessor and associated programming to analyse the results of the comparisons.
[0025] In a further embodiment the left-right load balance during scale entry and exit is
ignored.
[0026] In another embodiment when performing a center of gravity analysis:
- load cell pair data is used;
- load cell spacing in the direction of travel is either known or a uniform spacing
is assumed; and
- there is hysteresis in the evaluation of forward motion to prevent false triggers.
[0027] In a further embodiment a constant left-right load balance is indicated when the
ratio of the sum of all of the left side load cell weight readings to the sum of all
of the right side load cell weight readings remains substantially constant.
[0028] In another embodiment the expected state of each load cell output during a given
portion of a typical vehicle weighing operation is based on an expected pattern of
vehicle movement, the pattern of movement being:
- the vehicle enters an initially empty vehicle scale and moves along the scale platform;
- the vehicle either moves to a stopped position for weighing or exits the scale platform
, with or without a temporary start and restart of movement;
- while in the stopped position, cargo or other permissible items may be added to or
removed from the vehicle; and
- upon leaving the stopped weighing position, the vehicle moves along the scale platform
until the vehicle exits the scale.
[0029] In a further embodiment a load cell is determined to be operating improperly only
after an actual state condition of the load cell differs from an expected state condition
of the load cell some predetermined number of times within some predetermined time
period and then a notice of improper load cell operation is provided.
[0030] Another embodiment further comprises providing notice of improper load cell operation
when a trend of unexpected load cell state conditions or unexpected gross weight reading
states is detected.
[0031] In a further embodiment the notice of improper load cell operation is in the form
of an alert transmitted to one or more persons or in the form of a log file entry.
[0032] A further embodimentof the method of evaluating the operational condition a given
load cell of a vehicle weighing scale, the scale having a scale platform supported
from beneath by multiple load cells that are arranged in pairs in two spaced apart
rows that are aligned in the direction of normal vehicle travel across the scale platform,
the method comprises:
- identifying a dynamically changing, normal weight transfer pattern of behavior associated
with the outputs of pairs of load cells as a result of expected vehicle movement along
the scale platform during a typical vehicle weighing operation, each pair of load
cells comprising a first load cell from one row of load cells and a second load cell
from the other row of load cells that resides at a like distance from a given end
of the scale platform as the first load cell;
- ascertaining from the weight transfer patterns of behavior the expected state condition
for each of the load cells of the scale and the expected state of a gross weight reading
produced by the load cells, for different vehicle positions that will normally exist
during a typical vehicle weighing operation;
- detecting the presence of a vehicle on the scale when a gross weight reading provided
by the load cells exceeds a predetermined threshold weight;
- applying tests for determining proper load cell operation based on the expected load
cell pair output state conditions, the tests expecting that:
- all of the load cells will experience at least one load-unload cycle per vehicle,
- the load applied by the vehicle being weighed will be initially applied to the load
cells in a sequential, direction-of-travel order,
- the left-right load applied by the vehicle being weighed will be encountered by the
load cell pairs substantially simultaneously,
- the load center of gravity applied by the vehicle will move monotonically in the direction
of travel, and
- the left-right load balance on the load cell pairs will remain substantially constant;
- using a microprocessor and associated programming to analyze, against the test criteria,
the actual load cell output state conditions observed during a given vehicle weighing
operation, and to provide test results;
- identifying, with the microprocessor and associated programming, improper load cell
operation when a trend of unexpected load cell state conditions is detected; and
- providing notice of improper load cell operation.
[0033] In addition to the features mentioned above, other aspects of the invention will
be readily apparent from the following descriptions of the drawings and exemplary
embodiments, wherein like reference numerals across the several views refer to identical
or equivalent features, and wherein:
- Fig. 1
- schematically illustrates an exemplary vehicle weighing scale having a plurality of
load cells;
- Fig. 2
- is a flow chart that represents the expected movement of a vehicle on a vehicle weighing
scale during a vehicle weighing operation;
- Fig. 3
- is reflective of an exemplary state machine and associated thresholds that are created
for each load cell of a vehicle weighing scale according to method embodiments hereof;
- Fig. 4
- is an exemplary inferred vehicle position/state table that may be created according
to method embodiments hereof;
- Fig. 5
- is a table indicating exemplary data logging and analysis activities to be performed
in conjunction with various vehicle positions during a typical vehicle weighing operation.
[0034] Method embodiments of the invention may be used to analyze the dynamically changing
patterns of measurement values seen at each load cell of a vehicle weighing scale
as a vehicle traverses the scale platform of the scale during a normal vehicle weighing
operation. This analysis may be used to determine whether a load cell is operating
properly and/or being manipulated to produce a false weight reading.
[0035] An exemplary vehicle weighing scale 5 is depicted in FIG. 1 for purposes of further
describing exemplary embodiments of the invention. The scale 5 is shown to include
a scale platform 10 that is supported from beneath by a plurality of load cells LC1-LC8.
The load cells LC1-LC8 are arranged in two spaced apart rows R1, R2 aligned in the
direction of normal vehicle travel across the scale platform 10. Corresponding load
cells from each row R1, R2 (i.e., LC1-LC2, LC3-LC4, LC5-LC6, and LC7-LC8) are considered
to form load cell pairs based on load application during a vehicle weighing operation.
[0036] As indicated in FIG. 1, vehicles to be weighed may travel across the scale platform
10 in either direction - meaning that either end of the scale 5 is capable of serving
as the entry point. However, in normal practice, vehicles will always enter the scale
5 at one end and exit at the opposite end. For purposes of illustration, and not limitation,
the left side (end) of the scale 5 is designated herein as the normal entry end, as
indicated by the designators LC1 and LC2 for the initial pair P1 of load cells to
be loaded as a result of a vehicle entering from the left end of the scale.
[0037] When a vehicle enters, stops, is optionally loaded or unloaded, and exits the scale
5, the load cells LC1-LC8 will exhibit a pattern of measurement behavior that results
in various state transitions. These patterns of measurement behavior will change dynamically
as the vehicle moves across the scale. The dynamically changing patterns of behavior
may be observed with respect to the scale 5 when it is known that the load cells LC1-LC8
have not been tampered with and are working properly, in order to establish a normal
pattern of behavior. Subsequently, the dynamically changing patterns of measurement
values seen at the load cells of the scale 5 or of a substantially similar vehicle
weighing scale of interest, may be compared against the established normal pattern
of load cell behavior to determine whether a given load cell measurement is indicative
of improper load cell operation and/or a load cell that is being manipulated to produce
a false weight reading.
[0038] More specifically, established normal patterns of load cell behavior and associated
load cell state transitions for a given scale may be used as tests of proper load
cell operation for the same scale at some subsequent point in time. The same tests
may also be used to assess the load cell operation of other comparable scales.
[0039] As described above, the tests operate on the premise of the truth of a number of
assumptions, the expected normal behavior of the load cells during a typical vehicle
weighing operation, and the corresponding expected movement of the vehicle across
the scale. The assumptions and expected behavior of a given weighing scale are associated
with the scale construction and the operation of the load cells during a normal vehicle
weighing operation.
[0040] A first assumption is that the scale is normally not loaded. That is, the scale platform
is normally empty unless a vehicle is placed on the scale platform for the purpose
of a weighing operation. Another assumption according to method embodiments hereof
is that only a vehicle and its cargo will be weighed during a given vehicle weighing
operation. In this regard, there is considered to be no normal use case in which a
load is deposited on or removed from the scale platform without a vehicle first entering
the scale. Additionally, while cargo may be added or removed from the vehicle being
weighed, such activity may occur only when the vehicle is stopped on the scale platform.
It is further assumed that vehicles to be weighed enter the scale at one end and exit
at the opposite end and that vehicles do not intentionally reverse direction (i.e.,
back up) while on the scale platform.
[0041] FIG. 2 graphically describes an expected pattern of vehicle travel during a typical
vehicle weighing operation. The load cells of a vehicle weighing scale are expected
to undergo various state transitions that coincide with the changes in vehicle position/state
described in FIG. 2.
[0042] The vehicle travel pattern 15 of FIG. 2 begins with a vehicle entering an initially
empty vehicle scale and moving along the scale platform. The vehicle either moves
to a stopped position for weighing or exits the scale platform if, for example, the
weighing operation is aborted. As indicated in FIG. 2, it is also possible, prior
to reaching a stopped weighing position on the scale platform, for a vehicle to temporarily
stop and restart movement.
[0043] Once the vehicle stops moving on the scale platform, and as long as the vehicle remains
stopped, cargo or other permissible items may be added to or removed from the vehicle.
As should be obvious, the addition or removal of cargo will affect the load experienced
by the load cells and the weight readings produced thereby, assuming that the load
cells are operating properly and have not been tampered with.
[0044] Upon leaving the stopped weighing position (e.g., after weighing), the vehicle will
normally move along the scale platform until the vehicle exits the scale. The scale
will then return to an empty state, as reflected in FIG. 2.
[0045] As should be well understood by one of skill in the art, properly functioning and
non-manipulated load cells of the scale should exhibit an expected (normal) pattern
of behavior during vehicle movement and a corresponding weighing operation. In regard
to the aforementioned normal patterns of behavior, it is first expected that all of
the load cells will experience at least one load-unload cycle for each vehicle weighing
operation performed. Any load cell that does not move during a weighing operation
is likely in error. This conclusion is premised on certain caveats, said caveats being
that (1) a minimum load threshold is required for triggering load cell activity; and
(2) the analysis of load cell activity requires the presence of a vehicle, which is
indicated when the gross weight > threshold weight.
[0046] Because a vehicle always enters a scale from one of two ends, another expected pattern
of behavior is that the load of the vehicle should be initially applied to the load
cells in a sequential, direction-of-travel order. In other words, one end-pair of
load cells (i.e., P1 in FIG. 1) will always experience a load first, then the next
pair, and so forth (e.g., pair LC3-LC4 in FIG. 1, followed by pair LC5-LC6, and then
pair LC7-LC8). This expected behavior is also premised on certain caveats, said caveats
being that (1) load cells are evaluated in pairs for purposes of time stamping according
to method embodiments hereof; (2) a minimum load threshold is required for triggering
load cell pair evaluation; (3) only the first loading order is evaluated - load cells
may load-unload several times per vehicle; and (4) the analysis of load cell activity
requires the presence of a vehicle, which is indicated when the gross weight > threshold
weight.
[0047] It is also expected that the two load cells of a given load cell pair will simultaneously
experience a left-right load. That is, the two load cells of a load cell pair should
both see the leading edge of an axle loading or unloading almost simultaneously. Consequently,
a single load cell trigger when both load cells of a pair experience a load is likely
an error.
[0048] Furthermore, it is expected that the load center of gravity (COG) associated with
the vehicle being weighed moves monotonically in the direction of travel of the vehicle
while the vehicle is on the scale platform. That is, the load COG is generally expected
to move across the scale platform starting from one end, most likely stop, and then
exit at the other end without backing up. This expected behavior is premised on certain
caveats, said caveats being that (1) a one-dimensional center of gravity is calculated
in the direction of travel only, thus load cell pair data is used; (2) load cell spacing
in the direction of travel must either be known, or a uniform spacing should be assumed;
(3) there must be hysteresis in the evaluation of the forward motion to prevent false
triggers; (4) the analysis of load cell activity requires the presence of a vehicle,
which is indicated when the gross weight > threshold weight; and (5) a COG analysis
should not be performed during loading or unloading activity on the scale.
[0049] Lastly, it is also expected that the left-right load balance should remain constant
while the vehicle to be weighed remains fully on the scale platform. In other words,
while it is unlikely that a vehicle will present a symmetrically balanced transverse
(left-right) loading pattern while on the scale platform, the balance of left-right
load should at least remain constant within some tolerance range while the vehicle
is stopped and fully residing on the scale platform. Such a balanced left-right load
is indicated when the ratio of the sum of all of the left side load cell weight readings
to the sum of all of the right side load cell weight readings remains nearly constant.
As with several of the above-described conclusions, this conclusion is premised on
certain caveats, said caveats being that (1) the load imparted by the vehicle may
not be two-dimensionally symmetric and thus, the left-right balance during scale entry
and exit should be ignored; (2) a vehicle carrying a flowable load (e.g., a tanker
truck carrying a liquid) may present left-right oscillation due to shifting of the
load (e.g., sloshing liquid); and (3) the analysis of load cell activity requires
the presence of a vehicle, which is indicated when the gross weight > threshold weight.
[0050] Referring again to the exemplary scale 5 of FIG. 1, the various state transitions
experienced by the load cells LC1-LC8 as a vehicle crosses the scale as represented
in FIG. 2 may be used to create a mathematical model (state machine) that describes
an expected (normal) pattern of load cell behavior. This allows for, among other things,
the detection of the leading edge of each loading cycle to which a load cell is subjected.
A time stamp may be stored for each load cycle leading edge.
[0051] It should be noted that, due to the existence of multi-axle vehicles, multiple leading
edges might be seen during the weighing operation of a single vehicle. As illustrated
in FIG. 3, an Up Threshold value and a Down Threshold value is thus set for each load
cell. The Up Threshold value is associated with an increase in load borne by a load
cell as a vehicle to be weighed enters the scale. The Down Threshold value is associated
with a decrease in the load borne by the load cell as a vehicle to be weighed exits
the scale. The Up Threshold value is set higher than the Down Threshold value to prevent
false triggers when the load on a given load cell is close to the threshold value.
The load cell state machine is framed by the scale gross weight being greater that
its threshold weight.
[0052] The state transitions experienced by the load cells LC1-LC8 of the scale 5 may also
be used in conjunction with the gross weight value resulting from the combined load
cell weight readings, to create an inferred vehicle position/state table. One such
exemplary vehicle position/state table is shown in FIG. 4 as Table 1.
[0053] As can be understood from a reading of the heading row of Table 1, indications are
provided for expected vehicle position/activity ("Vehicle is"), gross weight reading
state, the state of the entry load cell pair, the state of the exit load cell pair,
the state of any load cell pair, and the state of all the load cell pairs. It is to
be understood that the headings of Table 1 are provided for descriptive purposes only,
and are not intended to be in any way limiting in nature. The vehicle position, as
well as the gross weight and load cell state, may be inferred from the logical AND
value of the conditions listed in the columns of Table 1.
[0054] A review of the "Vehicle is" column and the "Gross Weight" column of Table 1 reveals
that when there is no vehicle on the scale, the gross weight reading provided by the
load cells is expected to be less than the set threshold weight value. During the
time period that the vehicle is entering the scale, it is expected that the gross
weight reading will not decrease. While the vehicle is moving on the scale platform
or is stopped on the scale platform, it is expected that the gross weight reading
will be stable. If the vehicle is loaded while stopped on the scale platform, it is
expected that the gross weight reading will increase. Contrarily, if the vehicle is
unloaded while stopped on the scale platform, it is expected that the gross weight
reading will decrease. During the time period that the vehicle is exiting the scale,
it is expected that the gross weight reading will not increase.
[0055] A review of the "Vehicle is" column and the "Entry Pair", "Exit Pair", "Any Pair"
and "All Pairs" load cell state columns of Table 1 reveals an expectation that the
outputs of the entry load cell pair will be unstable while the vehicle is entering
the scale. Similarly, it is expected that the outputs of the exit load cell pair will
be unstable while the vehicle is exiting the scale. Furthermore, when the vehicle
is moving on the scale platform, it is generally expected that the outputs of one
or more load cell pairs of the scale will be unstable. Conversely, it is generally
expected that the outputs of all of the load cell pairs of the scale will be stable
when the vehicle is stopped on the scale platform, will not decrease while the vehicle
is loaded while on the scale platform, and will not increase while the vehicle is
unloaded while on the scale platform.
[0056] A state table (e.g., Table 1) produced according to method embodiments hereof is
graphically representative of the load cell state machine and reflective of the normal
pattern of behavior exhibited by the load cells and the gross weight load experienced
by the scale during a typical vehicle weighing operation. As such, the state conditions
of the state table may be used in one regard to infer vehicle position during a vehicle
weighing operation. For example, and referring to exemplary Table 1 for illustration,
if the output of the entry load cell pair of the scale of interest is unstable, it
is expected that the vehicle being weighed would be entering the scale at that point
in time.
[0057] Method embodiments of the invention are based on the understanding that a faulty
load cell, or a load cell that is being manipulated to produce false weight readings,
will generally fail one or more of the aforementioned tests. That is, the output of
a faulty or manipulated load cell will not reflect an established normal pattern of
load cell behavior during weighing operations of the scale. Such deviations from the
normal pattern of load cell behavior (i.e., test failures) may be used to evaluate
the condition of the load cell.
[0058] In regard to test failures, a single instance of a single load cell failing a single
test may be defined as an "event". Events are preferably counted and logged. A certain
number of events are to be expected, due to, for example, a forklift being driven
diagonally across the scale, or an unevenly loaded vehicle driving normally across
the scale. Multiple instances of the same event that are in excess of the number of
instances typically seen during normal scale operation may be defined as a "trend".
The normal operation event threshold is not zero and must either be learned by the
system or set by an installer. Trends must be evaluated over some time period (e.g.,
daily or weekly). A determination of improper load cell operation is not based on
an event, but rather on an observed trend.
[0059] System and method embodiments may operate to provide notice (an alert) of suspicious
load cell behavior. For example, an alert may be sent to an appropriate party, who
may or may not be the local operator. An alert may also be sent to various appropriate
parties. Alternatively, a system may be configured to never send alerts. For example,
a stored event log file or printed event log may ultimately be more useful than an
alert. In this case, a technician might evaluate such a log to determine system health
and make recommendations regarding possible repairs or changes to daily operating
procedures (e.g., keep forklifts off the scale, have someone watch a particular operator
for evidence of cheating, etc.).
[0060] Referring again to Table 1 for purposes of illustration, it can be understood how
the actual pattern of behavior of the gross weight value readings and the load cell
pair conditions during a given vehicle weighing operation can be compared against
the expected normal pattern of behavior of the gross weight value readings and the
load cell pair conditions, to determine whether a given load cell measurement is believable
and internally consistent (i.e., whether a load cell is operating properly and/or
being manipulated to produce a false weight reading). Particularly, the output of
a faulty load cell, or a load cell that is being manipulated to produce false weight
readings, will not match one or more of the expected state conditions listed in the
state table. For example, if the output of the entry pair of load cells remains stable
while a vehicle enters the scale, it may be assumed that the entry pair of load cells
are not operating properly or have been inappropriately manipulated. Similarly, if
the gross weight reading of a given load cell does not increase during loading of
a vehicle while the vehicle is on the scale, a faulty load cell(s) or an inappropriate
manipulation of a load cell(s) may also be indicated.
[0061] Time stamp data may be used to help determine vehicle location/state when evaluating
the load cell pair outputs for proper function. Exemplary time stamp operations are
described in Table 2 of FIG. 5, as are other exemplary functions that are preferably
associated with exemplary method embodiments hereof. For example, it can be seen that
when a scale becomes empty all existing time stamps should be cleared, and when the
vehicle enters the scale (i.e., the scale exits the "empty scale" state) a corresponding
time stamp and load cell entry pair output data should be stored. When a vehicle is
moving on the scale, Table 2 indicates that the last analysis results should be cleared
on vehicle entry, Test Cases 4-5 should be analyzed as the vehicle traverses the scale,
and the analysis results should be logged at vehicle exit. When the vehicle exits
the scale, Table 2 indicates that Test Cases 1-3 should also be analyzed and the results
should be logged.
[0062] A processor and associated programming are used to analyze the gross weight reading
and load cell or load cell pair output states in method embodiments hereof, and to
thereby determine whether the load cells of the scale are operating properly and/or
to detect a deliberate manipulation of the load cells. The programming may include
several algorithms for this purpose, with the algorithms executing on the processor.
The processor may be a part of a controller, such as a weighing scale controller.
The weighing scale controller may be in the form of a weigh terminal, such as for
example, a model IND780 weigh terminal available from Mettler-Toledo in Columbus,
Ohio. The load cells may be various types of digital load cells capable of reporting
the described information to the controller. For example, and without limitation,
the load cells may be Powercell® PDX® load cells also available from Mettler-Toledo,
and may be arranged as a Powercell PDX network of load cells.
[0063] While certain exemplary embodiments of the present invention are described in detail
above, the scope of the invention is not to be considered limited by such disclosure,
and modifications are possible without departing from the spirit of the invention
as evidenced by the following claims:
Reference signs list
[0064]
- 5
- Scale
- 10
- Scale platform
- 15
- Vehicle travel pattern
- P1
- Initial pair of load cells
- R1, R2
- Row of arranged load cells
1. A method of evaluating the condition of a given load cell of a multiple-load cell
vehicle weighing scale (5), comprising:
- identifying a dynamically changing, normal weight transfer pattern of behavior associated
with the outputs of each load cell during a typical operation of weighing a vehicle
on the vehicle weighing scale (5) or a like vehicle weighing scale (5);
- extracting from the weight transfer patterns of behavior, the expected state condition
for each of the load cells of the scale (5) for different vehicle positions that will
normally exist during a typical vehicle weighing operation;
- comparing the actual load cell state conditions observed during a given vehicle
weighing operation to the expected load cell state conditions; and
- analyzing the results of the comparison for each load cell to determine whether
a given load cell of the vehicle weighing scale (5) is operating properly.
2. The method of claim 1, further comprising:
- extracting from the weight transfer patterns of behavior, the expected state of
a gross weight reading produced by the load cells for different vehicle positions
that will normally exist during a typical vehicle weighing operation; and
- comparing the actual gross weight reading state conditions observed during a normal
vehicle weighing operation to the expected gross weight reading state conditions.
3. The method of claim 1, 2 or 3, wherein the expected state of each load cell output
during a given portion of a typical vehicle weighing operation is based on a plurality
of expected loading conditions, including:
- all of the load cells should experience at least one load-unload cycle per vehicle;
- the load applied by the vehicle being weighed should be initially applied to the
load cells in a sequential, direction-of-travel order;
- left-right load applied by the vehicle being weighed should be encountered by the
corresponding load cells substantially simultaneously;
- the center of gravity of the load applied by the vehicle should move monotonically
in the direction of travel; and
- the left-right load balance on the load cells should remain constant.
4. The method of claim 1 or 2, wherein the expected state of each load cell output during
a given portion of a typical vehicle weighing operation is based on an expected pattern
(15) of vehicle movement, the pattern (15) of movement being:
- the vehicle enters an initially empty vehicle scale (5) and moves along a platform
(10) of the scale (5);
- the vehicle either moves to a stopped position for weighing or exits the scale platform
(10), with or without a temporary start and restart of movement; and
- upon leaving the stopped weighing position, the vehicle moves along the scale platform
(10) until the vehicle exits the scale (5).
5. The method of one of the claims 1 to 4, wherein cargo or other permissible items may
be added to or removed from the vehicle while the vehicle is in the stopped position.
6. The method of one of the claims 1 to 5, wherein any load cell output that does not
move during a weighing operation is considered an error.
7. The method of one of the claims 1 to 6, wherein a load cell output analysis may not
be performed unless the gross weight reading value provided by the load cells is greater
than a predetermined threshold weight reading value that is representative of the
load borne by the load cells when the scale (5) is in an unloaded state.
8. A method of evaluating the operational condition a given load cell of a vehicle weighing
scale (5) according to claim 2, wherein the scale having a scale platform (10) supported
from beneath by multiple load cells that are arranged in pairs (P1) in two spaced
apart rows that are aligned in the direction of normal vehicle travel across the scale
platform (10), the method further comprising:
- identifying a dynamically changing, normal weight transfer pattern of behavior associated
with the outputs of each load cell during a typical operation of weighing a vehicle
on the vehicle weighing scale (5) or a like vehicle weighing scale (5);
- extracting from the weight transfer patterns of behavior the expected state condition
for each of the load cells of the scale (5) and the expected state of a gross weight
reading produced by the load cells, for different vehicle positions that will normally
exist during a typical vehicle weighing operation;
- using a microprocessor and associated programming to compare the actual load cell
output state conditions and the actual states of the gross weight reading produced
by the load cells during a given vehicle weighing operation to the expected load cell
output state conditions and expected states of the gross weight reading; and
- using the microprocessor and associated programming to analyze the results of the
comparisons. -.
9. The method of claim 8, wherein the left-right load balance during scale entry and
exit is ignored.
10. The method of one of the claims 8 or 9, wherein when performing a center of gravity
analysis:
- load cell pair (P1) data is used;
- load cell spacing in the direction of travel is either known or a uniform spacing
is assumed; and
- there is hysteresis in the evaluation of forward motion to prevent false triggers.
11. The method of one of the claims 3 or 8 to 10, wherein a constant left-right load balance
is indicated when the ratio of the sum of all of the left side load cell weight readings
to the sum of all of the right side load cell weight readings remains substantially
constant.
12. The method of one of the claims 8 to 11, wherein the expected state of each load cell
output during a given portion of a typical vehicle weighing operation is based on
an expected pattern (5) of vehicle movement, the pattern of movement being:
- the vehicle enters an initially empty vehicle scale (5) and moves along the scale
platform (10);
- the vehicle either moves to a stopped position for weighing or exits the scale platform
(10), with or without a temporary start and restart of movement;
- while in the stopped position, cargo or other permissible items may be added to
or removed from the vehicle; and
- upon leaving the stopped weighing position, the vehicle moves along the scale platform
(10) until the vehicle exits the scale.
13. The method of one of the claims 1 to 12, wherein a load cell is determined to be operating
improperly only after an actual state condition of the load cell differs from an expected
state condition of the load cell some predetermined number of times within some predetermined
time period and then a notice of improper load cell operation is provided.
14. The method of one of the claims 1 to 13, further comprising providing notice of improper
load cell operation when a trend of unexpected load cell state conditions or unexpected
gross weight reading states is detected.
15. The method of claim 13 or 14, wherein the notice of improper load cell operation is
in the form of an alert transmitted to one or more persons or in the form of a log
file entry.